This invention relates to a barometer utilizing a piezoelectric oscillator.
It is known that the a.c. voltage of a piezoelectric oscillator which is disposed inside a pressure vessel and causes bending oscillation at a series resonant frequency, changes with pressure as shown in FIG. 2. Therefore, if this a.c. resistance value is known, the pressure corresponding to the resistance value can be known.
Various methods of measuring the a.c. resistance value are known, and a typical example is shown in FIG. 3. An oscillator 1 generates an a.c. voltage e.sub.s of a frequency f. Reference numerals 2 and 3 represent an element to be measured and an amplifier, respectively. They constitute a current-voltage converter together with a feedback resistor R.sub.F, and the output voltage of the converter is e.sub.o. The amplifier is selected so that a current i.sub.x, flowing through the element to be measured, and a current i.sub.F, flowing through the feedback resistor, are equal. According to this system, the a.c. resistance Z.sub.x of the element to be measured is determined by the equation (1): EQU Z.sub.x =R.sub.F (e.sub.s /e.sub.o) (1)